Microelectronic devices, such as integrated circuit devices, are widely used in consumer, commercial and other applications. A microelectronic device generally includes a substrate, such as a semiconductor substrate, that includes therein/thereon a large number of active devices, such as transistors, and passive devices, such as resistors and capacitors. A wiring structure on the substrate is used to selectively electrically connect the active and/or passive devices to form circuits.
As the integration density of microelectronic devices continues to increase, and the performance of microelectronic devices continues to increase, the active and passive devices and the wiring structure may continue to scale down. Such scaling down may increase the number of interconnections in the wiring structure, which may produce more defects and/or decrease the production yield of the microelectronic device. Scaling down of the wiring structure may also increase the resistance thereof, which can decrease performance. Scaling down of the wiring structure may also increase the aspect ratios thereof, which may increase the difficulty of the fabrication process and thereby reduce the yield and/or reliability of the microelectronic devices. Finally, scaling down of the wiring structure may produce a smaller cross-section thereof, and increased performance requirements may cause the wiring structure to operate at higher frequencies, which may increase electromigration issues.
Wiring structures of microelectronic devices often are fabricated using a damascene process in which an underlying insulating layer is patterned with open trenches and/or vias where a conductor will be formed. A thick metal layer (e.g., copper) that significantly overfills the trenches and vias is deposited on the insulating layer, and Chemical-Mechanical Planarization (CMP) is used to remove the metal that extends above the top of the insulating layer. Metal sunken within the insulating layer is not removed, and becomes the patterned conductor. Single-damascene processes generally form and fill a single feature, such as a trench or via, with metal. Dual-damascene processes generally form and fill two features with metal at once. For example, a via and a trench overlying the via may both be filled with a single metal deposition using dual damascene.